1. Field of the Invention
The invention relates to a hydrodynamic torque converter.
2. Discussion of the Prior Art
A torque converter of the type mentioned above is known, for example, from German reference DE 195 27 853 A1, which has a converter circuit formed of an impeller wheel, a turbine wheel and a stator wheel. A driver for the piston of a lockup clutch is fastened to the turbine shell of the turbine wheel. The piston is mounted so as to be rotatable in the circumferential direction and displaceable in the axial direction. In the circumferential area, the piston has an axial shoulder which is directed to the driver and which has recesses at its free end that are uniformly distributed along the circumference. The projections provided at the driver in the radial circumferential region engage in the recesses without play in the circumferential direction. As a result of this driver, the turbine wheel is connected with the piston so as to be fixed with respect to rotation relative to it, so that torque which is transferred from the converter housing to the piston via a friction facing at the piston is transferred via the driver to the turbine wheel and, from the turbine wheel, to a driven shaft via an internal toothing.
It is disadvantageous in a driver of the type mentioned above that when the torque, which is often very high, is transmitted there is considerable surface area pressing at the sides of each recess at the axial shoulder of the piston and at the sides of the associated projection at the driver, which sides are in a working connection with one another, so that wear results very quickly at these contact surfaces. This has the undesirable result that the axial displacement capability of the piston is impeded.
For the transfer of high torque, the projections at the driver must be correspondingly wide in the circumferential direction. The rotational connection between the turbine wheel and the piston is therefore rigid, so that, along with the torque introduced by the converter housing, torsional vibrations which are superposed on the torque reaching the piston are transmitted to the turbine wheel without being filtered. In order to alleviate this problem, torsional damping devices with springs extending in the circumferential direction and, as the case may be, with at least one friction device are added, resulting in a sharp increase in the manufacturing costs and space requirement for the lockup clutch in the torque converter. Another solution consists in operating the piston with slip relative to the converter housing so as to reduce the torsional vibrations in this way through friction. This has the disadvantage of a comparatively high loss of output and an increased demand for guiding off the occurring frictional heat in order to prevent overheating of the converter components in the area of extension of the friction surface.